Conventional refrigeration based heat pump systems that respond to differing requirements for air heat may vary the amount of refrigerant flowing through a condenser exposed to a supply airstream in order to manipulate the temperature of the supply air. This can be accomplished with binary or modulating valves that divert a portion or all of the high pressure gas associated with the refrigerant flow through the condenser disposed in the airstream. One or more additional condensers are commonly used to reject the thermal energy present in the bypass gas or the refrigerant gas that is diverted around the refrigerant condenser in the supply airstream.
Requirements for increasing or decreasing the temperature of the supply air may be based directly or indirectly on a condition in the room with which the conditioned air is introduced or based solely on a measurement of temperature of the supply air either before or after interaction with the air stream condenser.
Commonly, control of the supply air temperature has been accomplished by diverting the discharge gas through the refrigerant condenser that is disposed in the supply air airstream or flow path. Commonly, a three-way valve is positioned to either bypass the refrigerant flow around the refrigerant condenser coil located in the supply airstream or divert the refrigerant through the condenser. This three-way valve can be of a binary control wherein the entire refrigerant flow is directed either through the condenser or through the condenser bypass passage. Others manipulate the thermal exchange between the refrigerant flow and the supply air flow by utilization of a modulating three-way valve capable of diverting only a portion of the refrigerant flow compressor discharge gas through the refrigerant condenser disposed in the supply airstream while diverting the remainder through the bypass line.
Diverting the compressor discharge gas through the refrigerant condenser in the supply airstream may be accomplished with two-way valves located in the refrigerant lines coupled to the refrigerant condenser and located in the bypass line. As in the case of the three-way valve, these valves may be of the binary or modulating type.
Still others modulate the discharge temperature through the use of dampers that divert airstream airflow through the supply air stream condenser or bypass the condenser in the supply airstream as required to increase and/or decrease the temperature of the airstream as desired.
Those prior art systems with multiple refrigerant condensers are subject to varying compressor discharge pressures and temperatures dependant on the temperatures and flow rates of the heat transfer mediums over all refrigerant condensers disposed in the system. The varying compressor discharge pressures creates difficulty in maintaining a desired temperature of the supply air during specific conditions, particularly as the temperatures of the heat transfer mediums decrease, the flow rates of the heat transfer mediums increase, and/or the requirements for increased temperature rise in the supply air. In the case of a system or condition where higher air temperatures are desired, the heat transfer taking place in one or more of the refrigerant condensers may be undesirable if such conditions cause the refrigerant pressure and temperature to drop to a point where the refrigerant and air stream heat transfer capability are limited by the parameters of the supply air steam condenser during air stream heating demands.
Still others make use of refrigerant discharge pressure controls in order to maintain a fixed discharge pressure. If used as a means for increasing supply air temperature, the fixed discharge pressure is typically determined by the highest supply air temperature requirements associated with a given application.
The higher discharge pressure control causes increased power consumption associated with operation of the compressor motor power which in turn detrimentally affects the total operating efficiency of the underlying system. During many times when requirements for supply air temperature are lower, it is advantageous to maintain discharge pressures as low as possible to improve the overall energy efficiency of the thermal exchange system. However, doing so may conflict with the heating demand requirements associated with the supply air temperature control.
Other methods of attempting to satisfy an air conditioning demand may include provisions for additional auxiliary heating of the supply air separate from the refrigeration circuit. The inclusion of such additional auxiliary heat requires additional energy to raise the temperature of the supply air and increases the cost and complexity of the construction of the resultant system. The additional auxiliary heating also increases the total energy consumption of the system and thereby detracts from the underlying efficiency associated with operation of the system.
Although some conventional systems may also control refrigerant system discharge pressures to allow for proper function of other system valves, controls, and refrigerant compressors, such controls are commonly associated with a fixed parameter value and are commonly also detrimental to the overall efficiency associated with operation of the system.